Variously configured devices of the pre-cited type are known in the technical field and depending on their principle of operation, they can be divided into so-called axial piston adjusting devices and so-called vane-type adjusting devices. In the case of axial piston adjusting devices, the hydraulically actuated adjusting element is constituted by an axially displaceable adjusting piston which cooperates with helical gears on the element attached to the crankshaft and on the element attached to the camshaft, while in vane-type adjusting devices, the hydraulically actuated element is constituted by a number of radial vanes on the element attached to the camshaft which are displaceable within pressure chambers in the element attached to the crankshaft.
On starting of an internal combustion engine configured with such a vane-type or axial piston adjusting device, the problem arises that the respective adjusting element moves at a high speed into a position of maximum displacement in which its repeated abutting is accompanied by a considerable amount of noise. This is due to the fact that when the engine has been turned off, the hydraulic medium contained in the device gradually escapes therefrom so that the adjusting element is no longer sufficiently supported hydraulically. Due to the torsional vibrations of the camshaft, the adjusting element, because of a lack of hydraulic support, is displaced into an end position on re-starting of the internal combustion engine, with the already mentioned considerable noise generation.
To avoid such noise generation, the solution disclosed in DE-OS 196 08 652 for an axial piston adjusting device proposes arranging in one of the two pressure chambers of the device, a slide which is mounted secure against rotation relative to a part of the housing connected to the drive pinion and which, with falling hydraulic medium pressure can be locked positively or by force with the element attached to the camshaft by the force of a compression spring.
A drawback of this solution which is suitable only for axial piston adjusting devices is, however, that the compression spring required for displacing the slide must have a relatively large diameter and, due to the restricted space in the device, cannot have more than a few turns. It is known from practice that such compression springs are relatively difficult and expensive to manufacture and thus, disadvantageously, increase the work and cost involved in the manufacture of the device. In the same way, the complicated procedure for the mounting of the slide inside the device and for the mounting of the parts cooperating therewith has proved to be relatively time-consuming and cost-intensive.
To avoid the mentioned noise generation in so-called vane-type adjusting devices, in contrast, DE-OS 196 23 818 discloses a solution which proposes arranging a locking pin in one of the vanes of the device, which pin is displaceable in a direction parallel to the central longitudinal axis of the device and, with falling hydraulic medium pressure, is pushed by the force of a compression spring into a locking opening in an end plate of an element attached to the crankshaft. This locking opening is in hydraulic communication with one of the pressure chambers so that the hydraulic medium pressure developing after the start of the internal combustion engine also acts on the end face of the locking pin and pushes the locking pin into its unlocking position in the vane.
A drawback of this solution which, in turn, is only suitable for vane-type adjusting devices, is that, for construction reasons, the end face of the locking pin which acts as a piston end surface is relatively small so that, for unlocking the locking pin, a relatively high hydraulic medium pressure has first to be built up. This has the result that, compared to axial piston adjusting devices, the unlocking of the locking pin is effected with some delay which can only be compensated by implementing expensive dimensioning measures on the rest of the hydraulic components.